rfc3314.txt

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   local addresses.  Site-local addressing allows communication to be
   administratively contained within a single site.  Link-local or
   site-local connections may also survive changes to global prefix
   information (e.g., site renumbering).

   IPv6 explicitly associates each address with an interface.
   Multiple-interface hosts may have interfaces on more than one link or
   in more than one site.  Links and sites are internally identified
   using zone identifiers.  Proper routing of non-global traffic and
   proper address selection are ensured by the IPv6 scoped addressing
   architecture [SCOPARCH].



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   IPv6 introduces the concept of privacy addresses [PRIVADDR].  These
   addresses are generated from an advertised global prefix and a
   randomly generated identifier, and are used for anonymous access to
   Internet services.  Applications control the generation of privacy
   addresses, and new addresses can be generated at any time.

   The IPv6 site renumbering specification [SITEREN] relies upon the
   fact that IPv6 nodes will generate new addresses when new prefixes
   are advertised on the link, and that they will deprecate addresses
   that use deprecated prefixes.

   In the future, additional IPv6 specifications may rely upon the
   ability of IPv6 nodes to use multiple prefixes and/or multiple
   identifiers to dynamically create new addresses.

1.5 An IP-Centric View of the 3GPP System

   The 3GPP specifications define a Third Generation Mobile System.  An
   overview of the packet switched (PS) domain of the 3GPP Release 99
   system is described in the following sections.  The authors hope that
   this description is sufficient for the reader who is unfamiliar with
   the UMTS packet switched service, to understand how the UMTS system
   works, and how IPv6 is currently defined to be used within it.

1.5.1   Overview of the UMTS Architecture

   The UMTS architecture can be divided into two main domains -- the
   packet switched (PS) domain, and the circuit switched (CS) domain.
   In this document, we will concentrate on the PS domain, or General
   Packet Radio Services (GPRS).

  ------
 |  TE  |
  ------
    |
    +R
    |
  ------   Uu  -----------   Iu  -----------   Gn  -----------   Gi
 |  MT  |--+--|   UTRAN   |--+--|   SGSN    |--+--|   GGSN    |--+--
  ------       -----------       -----------       -----------
   (UE)

                   Figure 1:  Simplified GPRS Architecture








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  ------
 |      |
 |  App |- - - - - - - - - - - - - - - - - - - - - - - - -(to app peer)
 |      |
 |------|                                              -------------
 |  IP  |- - - - - - - - - - - - - - - - - - - - - - -|      IP     |->
 | v4/6 |                                             |     v4/6    |
 |------|      -------------       -------------      |------       |
 |      |     |  \ Relay /  |     |  \ Relay /  |     |      |      |
 |      |     |   \     /   |     |   \     /   |     |      |      |
 |      |     |    \   /    |     |    \   /    |     |      |      |
 | PDCP |- - -| PDCP\ /GTP_U|- - -|GTP_U\ /GTP_U|- - -|GTP_U |      |
 |      |     |      |      |     |      |      |     |      |      |
 |------|     |------|------|     |------|------|     |------|      |
 |      |     |      |  UDP |- - -|  UDP |  UDP |- - -| UDP  |      |
 |      |     |      |------|     |------|------|     |------|      |
 |  RLC |- - -|  RLC |  IP  |- - -|  IP  |  IP  |- - -| IP   |      |
 |      |     |      | v4/6 |     | v4/6 | v4/6 |     |v4/6  |      |
 |------|     |------|------|     |------|------|     |------|------|
 |  MAC |     |  MAC | AAL5 |- - -| AAL5 |  L2  |- - -| L2   |  L2  |
 |------|     |------|------|     |------|------|     |------|------|
 |  L1  |- - -|  L1  |  ATM |- - -|  ATM |  L1  |- - -| L1   |  L1  |
  ------       -------------       -------------       -------------

    UE             UTRAN                SGSN                GGSN
 (handset)

                       Figure 2:  GPRS Protocol Stacks























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     ------
    |      |
    | App. |- - - - - - - - - - - - - - - - - - - - - - (to app peer)
    |      |
    |------|
    |      |
    |  IP  |- - - - - - - - - - - - - - - - - - - - - - (to GGSN)
    | v4/6 |
    |      |     |             |
    |------|     |-------------|
    |      |     |  \ Relay /  |
    |      |     |   \     /   |
    |      |     |    \   /    |
    |      |     |     \ / PDCP|- - - (to UTRAN)
    |      |     |      |      |
    |  PPP |- - -|  PPP |------|
    |      |     |      |  RLC |- - - (to UTRAN)
    |      |     |      |------|
    |      |     |      |  MAC |
    |------|     |------|------|
    |  L1a |- - -|  L1a |  L1b |- - - (to UTRAN)
     ------       -------------
       TE              MT
    (laptop)        (handset)

                 Figure 3:  Laptop Attached to 3GPP Handset

   The GPRS core network elements, shown in Figures 1 and 2, are the
   User Equipment (UE), Serving GPRS Support Node (SGSN), and Gateway
   GPRS Support Node (GGSN).  The UTRAN comprises Radio Access Network
   Controllers (RNC) and the UTRAN base stations.

   GGSN:  A specialized router that functions as the gateway between the
          GPRS network and the external networks, e.g., Internet.  It
          also gathers charging information about the connections.  In
          many ways, the GGSN is similar to a Network Access Server
          (NAS).

   SGSN:  The SGSN's main functions include authentication,
          authorization, mobility management, and collection of billing
          information.  The SGSN is connected to the SS7 network and
          through that, to the Home Location Register (HLR), so that it
          can perform user profile handling, authentication, and
          authorization.







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   GTP-U: A simple tunnelling protocol running over UDP/IP and used to
          route packets between RNC, SGSN and GGSN within the same, or
          between different, UMTS backbone(s).  A GTP-U tunnel is
          identified at each end by a Tunnel Endpoint Identifier (TEID).

   Only the most significant elements of the GPRS system are discussed
   in this document.  More information about the GPRS system can be
   found in [OLD-TS23060].

1.5.2   The PDP Context

   The most important 3GPP concept in this context is a PDP Context.  A
   PDP Context is a connection between the UE and the GGSN, over which
   the packets are transferred.  There are two kinds of PDP Contexts --
   primary, and secondary.

   The primary PDP Context initially defines the link to the GGSN.  For
   instance, an IP address is assigned to each primary PDP Context.  In
   addition, one or more secondary PDP Contexts can be added to a
   primary PDP Context, sharing the same IP address.  These secondary
   PDP Contexts can have different Quality of Service characteristics
   than the primary PDP Context.

   Together, a primary PDP Context and zero or more secondary PDP
   Contexts define, in IETF terms, a link.  GPRS links are point-to-
   point.  Once activated, all PDP contexts have equal status, meaning
   that a primary PDP context can be deleted while keeping the link
   between the UE and the GGSN, as long as there are other (secondary)
   PDP contexts active for the same IP address.

   There are currently three PDP Types supported in GPRS -- IPv4, IPv6,
   and PPP.  This document will only discuss the IPv6 PDP Type.

   There are three basic actions that can be performed on a PDP Context:
   PDP Context Activation, Modification, and Deactivation.  These
   actions are described in the following.

   Activate PDP Context

         Opens a new PDP Context to a GGSN.  If a new primary PDP
         Context is activated, there is a new link created between a UE
         and a GGSN.  A UE can open multiple primary PDP Contexts to one
         or more GGSNs.

   Modify PDP Context

         Changes the characteristics of a PDP Context, for example QoS
         attributes.



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RFC 3314       Recommendations for IPv6 in 3GPP Standards September 2002


   Deactivate PDP Context

         Deactivates a PDP Context.  If a primary PDP Context and all
         secondary PDP contexts associated with it are deactivated, a
         link between the UE and the GGSN is removed.

   The APN is a name which is logically linked to a GGSN.  The APN may
   identify a service or an external network.  The syntax of the APN
   corresponds to a fully qualified domain name.  At PDP context
   activation, the SGSN performs a DNS query to find out the GGSN(s)
   serving the APN requested by the terminal.  The DNS response contains
   a list of GGSN addresses from which the SGSN selects one (in a
   round-robin fashion).

                 ---------                           --------
                |         |                         |  GGSN  |
                |         |           LINK 1        |        |
                |      -======== PDP Context A ========-   - - -> ISP X
                |         |                         |        |
                |         |                         |        |
                |         |                         |        |
                |       /======= PDP Context B =======\      |
                |      -  |           LINK 2        |  -   - - -> ISP Y
                |       \======= PDP Context C =======/      |
                |         |                         |        |
                |   MT    |                          --------
                |(handset)|
                |         |                          --------
  --------      |         |                         |  GGSN  |
 |        |     |         |           LINK 3        |        |
 |        |     |      -======== PDP Context D ========-     |
 |   TE   |     |         |                         |        |
 |(laptop)|     |         |                         |      - - -> ISP Z
 |        |     |         |           LINK 4        |        |
 |     -====PPP====-----======== PDP Context E ========-     |
 |        |     |         |                         |        |
 |        |     |         |                         |        |
  --------       ---------                           --------

           Figure 3:  Correspondence of PDP Contexts to IPv6 Links

1.5.3   IPv6 Address Autoconfiguration in GPRS

   GPRS supports static and dynamic address allocation.  Two types of
   dynamic address allocation are supported -- stateless, and stateful.
   Stateful address configuration uses an external protocol to connect
   to a server that gives the IP address, e.g., DHCP.




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RFC 3314       Recommendations for IPv6 in 3GPP Standards September 2002


   The stateless IPv6 autoconfiguration works differently in GPRS than
   in Ethernet networks.  GPRS nodes have no unique identifier, whereas
   Ethernet nodes can create an identifier from their EUI-48 address.
   Because GPRS networks are similar to dialup networks, the stateless
   address autoconfiguration in GPRS was based on PPPv6 [PPPV6].

   3GPP address autoconfiguration has the following steps:

      1. The Activate PDP Context message is sent to the SGSN (PDP
         Type=IPv6, PDP Address = 0, etc.).

      2. The SGSN sends a Create PDP Context message to the GGSN with
         the above parameters.

      3. GGSN chooses an interface identifier for the PDP Context and
         creates the link-local address.  It answers the SGSN with a
         Create PDP Context response (PDP Address = link-local address).

      4. The SGSN sends an Activate PDP Context accept message to the UE
         (PDP Address = link-local address).

      5. The UE keeps the link-local address, and extracts the interface
         identifier for later use.  The UE may send a Router
         Solicitation message to the GGSN (first hop router).